Method of determining variations in the morphology of a borehole

ABSTRACT

Method of determining variations in the morphology of a borehole. It consists in measuring, as a function of the depth of the borehole, the dip and the azimuth (a 1 ) of the borehole, the inside diameters of the borehole in two perpendicular directions, and the azimuth (a 2 ) of a reference caliper and it is characterized in that consists in determining the eccentricity (e m ), together with an eccentricity error (Δe m ), the azimuth (a 3 ) of the second caliper from the azimuth (a 2 ), and the rotation speed (V R ) of the reference caliper, and then comparing (Δe m ) to a threshold value (Δe s ) and (V R ) to a threshold value (V S  ) to determine the type of ovalization of the borehole.

This is a 371 of PCT/FR 94/00083 filed Jan. 24, 1994.

This is a 371 of PCT/FR 94/00083 filed Jan. 24, 1994.

BACKGROUND OF THE INVENTION

The present invention concerns a method of determining variations in themorphology of a borehole.

Electrical imaging of the borehole wall is increasingly being used todetermine the shape and the dimensions of said borehole. Electricalimages of the borehole wall are obtained by means of special-purposetools known as dipmeters including the FORMATION MICRO SCANNER (FMS)developed by SCHLUMBERGER.

A dipmeter such as the FMS has at its lower end means for emitting afocused electric current and pads which bear against the borehole wall.The electrical resistivities of said wall are measured using electrodeson each of said pads. The number of electrodes on each pad can vary fromone tool to another, in order to obtain better coverage of the boreholewall.

The FMS or equivalent measurement tool is designed to operate inconductive water-based mud, the scanning depth varying from 2.5 cm (1inch) to 15 cm (6 inches).

The tool has at its upper end at least one three-axis accelerometer andthree magnetometers for measuring the speed, the position and theorientation of the tool in each measurement period.

The logged measurements obtained using the tool can be processed, forexample to correct the speed and in particular to correct irregularmovement of the tool due to the tool jamming in the borehole, and tocorrect the current since the current emitted varies to maintain theoptimal resolution in the event of high contrast in the resistivity.

Further processing can also be applied, such as horizontal normalizationof the measurements and representation of the resistivity imagesrelative to a given azimuth direction, usually North.

The measurement tool described in outline above is used, among otherthings, to determine the direction of maximum stress that can deform thewall of the borehole. The generic term for this is "ovalization".

Due to in situ stresses of tectonic origin, the wall of a borehole tendsto scale in a preferred direction, creating eccentric voids of greateror lesser depth with their major axis perpendicular to the direction ofthe maximum horizontal stress. This phenomenon is known as "ovalizationby scaling".

If the direction of the maximum horizontal stress is known, thedirections in which cracked reservoirs drain are known more accurately,it is possible to predict the directions in which hydraulic fracturesdevelop, and some wall strength problems can be understood and solved.

Accordingly, attempts have been made to develop ovalization as a meansof detecting, orienting and quantifying deformation of the wall of aborehole, and above all to discriminate between the various types ofovalization to determine that which can indicate the orientation of themaximum horizontal stress, since there are several types of ovalizationthat are related to other types of deformation, of greater or lesserapparent similarity, but of different origins. These include wearovalization due to rubbing of the string of drill pipes against the wallof the borehole, ovalization due to the presence of structuraldiscontinuities such as stratification, fracturing, etc.

Unfortunately, existing techniques are not able to discriminate or todistinguish quickly and reliably the type of ovalization which canindicate the orientation of the maximum horizontal stress.

SUMMARY OF THE PRESENT INVENTION

Starting with the resistivity measurements obtained by means of thetool, it is necessary to make an empirical definition of the type ofovalization and then to determine if the latter ovalization matchespreliminary studies carried out by other means. If there is insufficientcorrespondence, then a different type of ovalization is defined and thisprocess is repeated until the appropriate ovalization is determined.

An object of the present invention is to propose a method of determiningvariations in the morphology of a borehole which determines the varioustypes of ovalization sequentially and, after viewing of the results on amedium, determines the type of ovalization which indicates theappropriate orientation of the maximum horizontal stress.

The present invention comprises a method of the type using a toolcomprising at least two calipers and measurement units and continuouslymeasuring by means of said tool and as a function of the depth

the dip and the azimuth (a₁) of the borehole in a geographical system ofaxes;

the inside diameters of the borehole in two perpendicular directions, bymeans of the two calipers, one of the inside diameters beingrepresentative of the greatest horizontal deformation of the borehole;

the azimuth (a₂) of a first caliper taken as a reference diameter in thesystem of axes of the borehole;

and further comprises:

continuously determining the eccentricity (e_(m)) of the borehole whichis representative of the ratio of the diameters of the borehole and ofthe eccentricity error Δe_(m) which is equal to 1-e_(m),

determining the azimuth (a₃) of the second caliper from the azimuth (a₂)of the reference first caliper in the system of axes of the borehole,

determining the variation in the azimuth (a₂) of the reference firstcaliper during displacement of the tool in the borehole in order todetermine the rotation speed (V_(R)) of said reference caliper duringsaid displacement,

comparing said eccentricity error (Δe_(m)) to a threshold value (Δe_(s))to define the presence of ovalization of the borehole when (Δe_(m)) isgreater than (Δe_(s)) and then specifying the type of ovalization bycomparing the rotation speed (V_(R)) to a threshold value (V_(S)).

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features of the invention will emerge more clearlyfrom a reading of the following description of one preferred embodimentof the invention and from the appended drawings in which:

FIG. 1a shows the ovalization of a borehole in an anisotropic stressfield.

FIG. 1b is a perspective view of the lower part of the tool includingfour pads.

FIG. 2 is a graphical representation initially cylindrical now flattenedout (unwound), showing the information logged from each pad, with thedark areas representing area of high conductivity.

FIG. 3 is a graphical representation showing three curves representingthe nominal diameter of the borehole and diameters measured by the toolin two perpendicular directions, as a function of depth.

FIG. 4 is a graphical representation showing the eccentricity determinedfrom the values of the two borehole diameters measured by the tool fromFIG. 1b, as a function of depth.

FIG. 5 is a graphical representation four curves which represent, as afunction of depth, the deviation of the borehole from the vertical (infull line), the direction of the deviation of the borehole, which isbetween 0° and 180° relative to North (in dashed line), the direction ofthe ovalization when it is below a predetermined threshold (in dottedline) and the direction of the ovalization when it is above thepredetermined threshold (thick dotted line).

FIG. 6 is a graphical representation showing a breakdown of theovalization areas in accordance with a representation code.

FIGS. 7a and 7b are two graphical image logs of the borehole, as afunction of depth, in two perpendicular directions and showing thetraces of the two pads.

FIG. 8 represents an unwound, initially cylindrical area for loggingchart the information logged from each pad.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to FIGS. 1a and 1b, a dipmeter type tool fitted withappropriate means as mentioned previously is lowered into a borehole ofnominal diameter φ on a cable that is not shown but which incorporatesall the necessary electrical and mechanical connections. Only the lowerpart of this tool is shown in figure 1b. The tool 2 includes at leastfour pads 3 through 6 which are coupled in pairs to constitute twocalipers 3, 5 and 4, 6 disposed in perpendicular directions. Onecaliper, for example the caliper 3, 5, measures the greatest horizontaldeformation of the borehole φ₁. The other caliper 4, 6 measures thedeformation φ₂ of the borehole perpendicular to the deformation φ₁.

Using magnetometers which are part of the tool, the deviation or dip ofthe axis 8 of the borehole from the vertical is determined. The azimutha₁ of the axis 8 of the borehole is also measured in a geographicalsystem of axes, together with the azimuth a₂ of the pad 3 which is takenas the reference pad, the azimuths a₁ and a₂ being expressed relative tomagnetic North, for example, and measured clockwise.

The eccentricity e_(m) of the borehole is determined continuously as thetool 2 is raised from a given low point in the borehole to a given highpoint in the borehole. The eccentricity e_(m) is determined by the ratioφ₂ /φ₁ where φ₁ is the largest diameter measured and φ₂ is the smallestdiameter measured. The eccentricity error Δe_(m) is calculated from theequation ##EQU1##

If the ratio φ₂ /φ₁ is equal to 1, the borehole can be assumed to becircular (Δe_(m) =0). If the ratio φ₂ /φ₁ is less than 1 (Δe_(m) >0),the cross-section of the borehole is oval in shape, like an ellipse. Inpractise the eccentricity e_(m) is between 1 and 0.25, the latter valuerepresenting a very high degree of ovalization. The threshold for theeccentricity error Δe_(s) is chosen arbitrarily, for example so that1-φ₂ /φ₁ =0.04; in this case, the eccentricity error threshold Δe_(s) isset at 4%, the eccentricity error Δe_(m) determined being compared withthis threshold value Δe_(s).

The azimuth a₃ of one of the pads, for example the pad 4 of the secondcaliper 4, 6, is determined from the azimuth a₂ of the reference pad andthe variation Δa₂ of the azimuth a₂ of the reference pad 3 is determinedcontinuously as the tool 2 is moved in the borehole 1 in order todetermine the rotation speed V_(R) of said pad 3 or (which amounts tothe same thing) that of the caliper 3, 5.

At another stage the eccentricity error Δe_(m) determined is compared toa predetermined threshold value Δe_(s) to eliminate the effects ofirregularities of the wall and, most importantly, of the accuracy of themeasurements effected by the calipers 3, 5 and 4, 6. This makes itpossible to determine whether the wall of the borehole is subject ofovalization or deformation.

The type of ovalization present in the borehole is determined bycomparing the rotation speed V_(R) with a predetermined threshold valueV_(S).

The error Δ_(a) between the azimuth a₁ of the borehole and the azimutha₂ or a₃ (the azimuth a₂ in the example shown) of the larger caliper iscompared, if necessary, with a predetermined minimum error value Δ_(a)min. The error Δ_(a) min is chosen according to the value of the dip ofthe borehole. Thus the farther the dip of the borehole departs from thevertical, the greater the action of the string of drill pipes and thegreater the error Δ_(a) min. For example, when the dip is:

i) greater than 10°, Δ_(a) min is equal to 30°,

ii) between 5° and 10°, Δ_(a) min is equal to 20°,

iii) less than 5°, Δ_(a) min is equal to 10°.

If the value of the rotation speed V_(R) is greater than thepredetermined threshold value V_(S) ovalization of the helical void typeis present.

If the value of the rotation speed V_(R) is less than the predeterminedthreshold value V_(S), then the error Δ_(a) is compared with Δ_(a) min.If Δ_(a) is greater than Δ_(a) min, the ovalization is of the scalingtype. If Δ_(a) is less than Δ_(a) min, the ovalization is of the weartype.

FIG. 2, lines 3a through 6a shows, in an unwound, initially cylindricalchart of the information logged from the four pads 3 through 6,respectively. The dark areas 20 represent areas of high conductivity.The lighter areas 21 represent low values of conductivity, i.e. highvalues of resistivity. The area 22 in which the direction of the tracechanges corresponds to an area of the borehole in which the measuringtool jammed momentarily, this corresponding to a borehole diameter equalto the nominal diameter φ for the area in question; this can also beseen in FIGS. 3, 7a and 7b in which at depth 3504 of the borehole thetwo measured diameters are equal (see 32 in FIG. 3) because of thevirtual superimposition of the two curves 30 and 31; in FIG. 4 theeccentricity 41 is very much lower than the predetermined threshold; inFIGS. 7a and 7b there is a constriction 70.

When the tool is guided there is no change of direction in the tracesand each change of direction indicates that the tool is no longer guidedand can turn, without resistance, as it is drawn upward by the cable.

At depth 3515 both traces 3a and 5a are light in colour (highresistivity) whereas the traces 4a and 6a are dark, showing highconductivity.

The width of the traces 4a and 6a is much less than that of the traces5a and 3a which indicates that at this location the borehole is subjectto ovalization and that the pads 4 and 6 are on the major axis of theoval. 0n the major axis of the oval the wall is subject to scaling, andmud permeating into the area subject to scaling makes the formation moreconductive than the same formation seen at the same depth by the pads 3and 5.

This can be seen in FIG. 3 in which the curve 31 representing thediameter measured by the pads 3 and 5 is close to the nominal diameter33 whereas the curve 30 representing the diameter measured by the pads 4and 6 is very far away from the nominal diameter. This corresponds to ahigh eccentricity error 42 in FIG. 4, very much greater than thepredetermined threshold 41.

Examination of FIGS. 3 and 4 shows that there is a perfectcorrespondence between the curves shown. The part 42 of FIG. 4 whichrepresents a high eccentricity, of almost 0.5, corresponds to a veryclear separation of the curves 30 and 31 in FIG. 3. The same phenomenon,although less accentuated, is seen in part 43 of FIG. 4, the curves 30and 31 from FIG. 3 being still far apart. On the other hand, the pointof contact of the part 32 of the curves 30 and 31 which are coincidentin the figure with the vertical 33 (nominal borehole diameter) showsclearly that there is no eccentricity and no voids whereas therespective parts 35 and 36 of curves 30 and 31 (depths 3500 to 3503)shows that the eccentricity is very slight (the curves 30 and 31 beingvery close together), but that there is a void since the diameter of theborehole is not the nominal diameter 33.

Between depths 3537 and 3541, the curves 30 and 31 are also very closetogether although in this case they are very far away from the nominalborehole diameter 33, which indicates that there is no or littleeccentricity but also indicates the presence of a void.

The corresponding aligned parts in FIG. 4 confirm the greater or lessereccentricity at the various depths in the borehole.

In FIG. 5 the line 50 represents an imaginary vertical axis. The curve51 shows the deviation of the borehole axis relative to the imaginaryvertical axis 50. Between depths 3507 and 3522 there is virtually nodeviation. At other depths in the borehole on either side of thoseindicated and visible in the figure, the deviation is less than 5°.

The dashed curve 52 represents the direction of the deviation 51relative to North, in the form of an angle between 0° and 180°. For thepart of the borehole between depths 3507 and 3522, the curve 52 includesa part 53 subject to high levels of fluctuation because the measuredazimuth in a sub-horizontal plane does not make sense mathematically orphysically. The parts 54 and 55 of the curve 52 indicate that thedirection of the deviation varies very little.

The dotted curve 56 shows the direction of the major axis of the ovalrelative to North, in the form of an angle between 0° and 180°.

Up to depth 3505, the part 59 of the curve 56 corresponding to an areaof the borehole indicates that the major diameter of the oval ismeasured alternately by the calipers 3, 5 and 4, 6. The same phenomenonoccurs between depths 3537 and 3541. Consequently, between depths 3505and 3537, on the one hand, and beyond depth 3541, on the other hand, thecurve 56 comprises two parts 57 and 58 which indicate a slight variationin the direction of ovalization, and the conclusion to be drawn fromthis is that the tool is turning very slightly in the borehole, the toolturning even less in the part 58 than in the area 57. However, therotation speed of the tool is higher in the lower end part of the area58 than in the area 57.

The thick dotted line curve in areas 57 and 58 represents ovalizationexceeding the predetermined threshold. The area 57 corresponds to theparts 42 and 43 of FIG. 4. Examining the parts of FIGS. 2, 3, 4 and 5corresponding to the parts 42 and 43 of FIG. 4 confirms the presence ofpure scaling.

The thick dotted curve in FIG. 5 corresponding to parts 42 and 43 ofFIG. 4 indicates a low speed of rotation of the tool, a low variation inthe speed of rotation of the tool and virtually no deviation of theborehole. Parts 42 and 43 of FIG. 4 indicate a very high eccentricityindicating a high amplitude of ovalization. Taken together, all thisinformation makes it virtually certain that scaling is present.

The irregularity of the curves 30 and 31 corresponding to the areas 42and 43 support the presence of ovalization by scaling.

With reference to these same parts 42 and 43, FIG. 2 can be used todetermine if scaling is present or not. In line with the parts 42 and43, the image logs for the pads 3 through 6 in the boreholedifferentiate conductivity differences between the pads. Considerportions 23 and 24 of traces 4a and 6a, for example: notice that theyare dark between depths 3504 and 3530, which shows high conductivity,whereas for the same depths the portions 25 and 26 of traces 3a and 5ashow lighter areas, indicating low conductivity or high resistivity. Theconclusion to be drawn from this is that there are cracks in the wall ofthe borehole which have been permeated by the conductive mud used as adrilling lubricant. Because the deformation of the borehole is due toovalization by cracking, it can be deduced that the ovalization of thewall of the borehole was caused by wall portions between cracks fallinginto the borehole, these portions being known as "scales".

FIG. 6 represents a synthesis of the information given by FIGS. 2through 5.

The area 60 is an area with no marked ovalization (part 59 of curve 56),with an eccentricity error below the threshold (part 41 of FIG. 4), andincluding at least one void (parts 35 and 36 of curves 30 and 31) whichindicates low cohesion of the materials constituting the rock present atthis depth.

Area 61 is an area of the borehole in which there is no deformation, thealigned curves 30 and 31 being practically coincident and the measuredborehole diameter being substantially equal to the nominal diameter.

Areas 62 and 63 are areas of marked ovalization, with very higheccentricity (FIG. 4), a low rotation speed of the tool (FIG. 5),virtually no deviation of the borehole axis (FIG. 5) and undoubtedscaling given the high conductivity in the direction of the major axisof the ellipse (FIG. 2), this direction being shown by a straight linesegment 62a in the case of area 62 at 75° relative to North (i.e.East-North East) and in the case of area 63 by a straight line segment63a at 110° relative to North (i.e. East-South East).

Area 64 is an area in which the eccentricity error is, overall, greaterthan the threshold (part 57 of curve 56), but relatively small, with asmall deviation of the borehole. Despite this small deviation of theborehole, there is some parallelism between the curve 56 and the curve52. The error Δ_(a) between these two curves is measured and thencompared to a predetermined error Δ_(a) min. Since Δ_(a) is greater thanbut close to Δ_(a) min, it can be deduced that scaling is probable. Ifthe error Δ_(a) is less than Δ_(a) min, then wear type ovalization ispresent. The straight line segment 64a represents the direction of themean major axis of ovalization in this area, this segment being at 140°relative to North (i.e. South-East).

The area 65 is an area in which the diameters measured by the calipersare substantially equal (curves 30 and 31 are practically superimposed),with a slight deviation in the direction of the borehole and a globaleccentricity below the threshold. Also, in the area in question, thecurves 52 and 56 are substantially parallel and the error Δ_(a) betweenthem is less than Δ_(a) min. The rotation speed V_(R) of the tool isdetermined, for example calculated, and then V_(R) is compared to apredetermined fixed value V_(S). In this area, V_(R) <V_(S) and becauseΔ_(a) is less than Δ_(a) min, the conclusion is that ovalization by wearis present.

Areas 66 and 67 are analogous to areas 62 and 63, i.e. to areas ofovalization by scaling, with no conductivity anomalies visible in FIG. 2and with ovalization major axis directions indicated by the respectivestraight line segments 66a and 67a; the segment 66a is at 30° North(North-East) and the segment 67a is at 35° North (North-East).

The area 68 is an area in which the eccentricity error is greater thanthe threshold, the tool rotation speed V_(R) is high and greater thanthe threshold V_(S) (change in direction of the curve 52) and Δ_(a)>Δ_(a) min. The conclusion to be drawn from this is the presence ofhelical void type ovalization caused by rotation friction of the drillpipe string in an area of low cohesion or in which the axis of theborehole is changing direction.

The curve used to generate the ovalization direction curve 56 issmoothed so as not to intersect the borehole at too many non-meaningfulareas of the lithology encountered.

FIGS. 7a and 7b show the diameters of the borehole as in twoperpendicular directions as a function of the depth.

Traces 70a through 71b show the walls of the borehole in the chosensection plane passing through the axis of the borehole, the distancesbetween these walls in a plane perpendicular to the section planerepresenting the apparent diameters of the borehole.

Traces 72 (FIG. 7a) and 73 (FIG. 7b) respectively correspond to pads 3and 5, the traces corresponding to pads 4 and 6 not being shown in FIGS.7a and 7b. FIGS. 7a and 7b show the eccentricity in all directionsthrough an appropriate choice of the section plane.

In accordance with another feature of the invention, the loggedinformation from the calipers 4, 6 and 3, 5 is viewed on any medium,such as a screen or a strip paper chart, in the form of an image log(see FIG. 8) comprising separate rectangular strips 80 through 83 ofvarying widths; each strip is the image of one pad of the calipers onthe unwound cylinder of diameter φ, said strip having a horizontaldimension or width 1 and a vertical dimension H representing therecordings at various depths.

FIG. 1a is a diagrammatic plan view of a circle representing theborehole of nominal diameter φ and an ellipse 9 representing theovalized deformation of the borehole, together with the four pads 3through 6.

Assuming a cylindrical initial volume, the information obtained fromeach pad 3 through 6 would be shown on the image log by strips ofidentical width, equal to:

L₁ =pad width×display scale.

The width of the image log would be equal to:

L=π×φ×display scale.

The representation on an image log of the information logged by each padin any non-cylindrical volume depends on the ratio between the nominaldiameter φ of the image log and the diameter φ_(e) logged by the pair ofpads including the pad in question.

The width L₁ of the image of a pad at a distance φ_(e) / 2 from the axisof the borehole or from the tool is equivalent on the image log ofradius φ/2 to 1=L₁. φ/φ_(e).

The strip width on the image log of diameter φ corresponding to a pad ata distance φ₁ /2>φ/2 is less than the width of the pad (to the nearestdisplay increment); likewise, the width of the strip corresponding to apad at a distance φ₁ /2<φ/2 is greater than the width of the pad.

The representation method is valid regardless of the number of pads andtheir width and whether the pads are linked in pairs or independent ofeach other. The relative position of the pads on an image log isobtained by a measurement specifying the position of one of the pads,the reference pad for example, in the system of axes of the borehole,the position of the other pads being calculated from the angular offsetbetween the pads.

The method of the invention can display the various measurements on amedium as a function of depth to produce borehole logs, the differenttypes of ovalization, depending on depth, being shown using arepresentation code, for example in the form of coloured areas in whicheach colour corresponds to a given type of ovalization (areas 60 through68 of FIG. 6, for example).

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

We claim:
 1. Method of determining variations in the morphology of aborehole, using a tool comprising at least first and second calipers,each of the calipers having a measurement unit, said method comprising:measuring by means of said tool and as a function of depththe dip andthe azimuth (a₁) of the borehole in a geographical system of axes; theinside diameters of the borehole in two directions, by means of thefirst and second calipers; and, the azimuth (a₂) of the first caliperdetermining the eccentricity (e_(m)) of the borehole, at a given depth,said eccentricity (e_(m)) being representative of the ratio of themeasured inside diameters of the borehole and of the eccentricity errorΔe_(m) =1-e_(m), determining the azimuth (a₃) of the second caliper fromthe azimuth (a₂) of the first caliper in the system of axes of theborehole, determining the variation in the azimuth (a₂) of the firstcaliper during displacement of the tool in the borehole in order todetermine the rotation speed (V_(R)) of said first caliper during saiddisplacement, comparing said eccentricity error (Δe_(m)) to a thresholdvalue (Δe_(s)) to define the presence of ovalization of the boreholewhen (Δe_(m)) is greater than (Δe_(s)) and then determining the type ofovalization by comparing the rotation speed (V_(R)) to a threshold value(V_(s)).
 2. Method according to claim 1 wherein if the rotation speed(V_(R)) is less than the threshold value (V_(s)) said method furthercomprises measuring the azimuth error (Δ_(a)) between the azimuth (a₁)of the borehole and the larger of the azimuth (a₂ or a₃) of the firstand second calipers, and then comparing said azimuth error (Δ_(a)) witha predetermined error value (Δ_(a) min).
 3. Method according to claim 2wherein the type of ovalization determined is scaling type ovalizationif the error (Δ_(a)) is greater than the error value (Δ_(a) min). 4.Method according to claim 2 wherein, the type of ovalization determinedis wear type ovalization if the error (Δ_(a)) is less than the errorvalue (Δ_(a) min).
 5. Method according to claim 1 wherein the type ofovalization determined is helical void type ovalization if the rotationspeed (V_(R)) is greater than the threshold value (V_(s)).
 6. Methodaccording to claim 1 wherein the curve representing variation in theazimuth (a₂) of the first caliper during displacement of the tool in theborehole is smoothed prior to determining the type of ovalization. 7.Method according to any one of claims 1 to 6, wherein the dip and theazimuth (a₁) of the borehole, the inside diameters of the borehole andthe azimuth (a₂), are viewed on a medium in the form of an image log,the image log comprises separate strips of varying width, each stripdisplaying at least one of the measurements.
 8. Method according toclaim 7 wherein the measurements are viewed on a medium as a function ofdepth, thereby producing borehole logs.
 9. Method according to claim 7wherein the type of ovalization is also viewed on a medium, on aseparate strip, as a function of the depth, using a representation codeto represent the type of ovalization.
 10. Method according to any one ofclaims 1 to 6 wherein the dip and the azimuth (a₁) of the borehole, theinside diameters of the borehole and the azimuth (a₂), are viewed on amedium as a function of depth thereby producing borehole logs. 11.Method according to any one of claims 1 to 6 wherein the types ofovalization are viewed on a medium as a function of the depth using arepresentation code.
 12. Method according to claim 11, wherein therepresentation code is a color code having each of a plurality of colorscorrespond to a type of ovalization.
 13. Method according to claim 7,wherein each of the calipers comprises a pair of caliper pads, and atleast one strip displays the image of the measurements of at least oneof the pair of caliper pads, and the width of the at least one strip isproportional to the width of the corresponding caliper pad and to theratio of the nominal diameter of the borehole to the diameter measuredby the caliper of which said caliper pad is part.